The following discussion of the background of the invention is merely provided to aid the reader in understanding the invention and is not admitted to describe or constitute prior art to the present invention.
Metalloproteinase inhibitor 2 (Swiss-Prot P16035, also known as “Tissue inhibitor of metalloproteinases 2” and “TIMP2”) is a secreted protein which complexes with metalloproteinases and irreversibly inactivates them by binding to their catalytic zinc cofactor. TIMP2 is known to act on MMP-1, MMP-2, MMP-3, MMP-7, MMP-8, MMP-9, MMP-10, MMP-13, MMP-14, MMP-15, MMP-16 and MMP-19. TIMP2 reportedly suppresses the proliferation of endothelial cells. As a result, the encoded protein has been suggested to have a role in the maintenance of tissue homeostasis by suppressing the proliferation of quiescent tissues in response to angiogenic factors, and by inhibiting protease activity in tissues undergoing remodeling.
In addition, WO2010/048346 and WO2011/075744, each of which is hereby incorporated by reference in its entirety including all tables, figures and claims, describe the use of TIMP2 for evaluating the renal status of a subject both individually and in multimarker panels. In particular, TIMP2 levels measured by immunoassay are shown to correlate to risk stratification, diagnosis, staging, prognosis, classifying and monitoring of the renal status.
Signals obtained from specific binding assays such as immunoassays are a direct result of complexes formed between one or more binding species (e.g., antibodies) and the target biomolecule (i.e., the analyte) and polypeptides containing the necessary epitope(s) to which the antibodies bind. Immunoassays are often able to “detect” an analyte; but because an antibody epitope is on the order of 8 amino acids, an immunoassay configured to detect a marker of interest will also detect polypeptides related to the marker sequence, so long as those polypeptides contain the epitope(s) necessary to bind to the antibody or antibodies used in the assay. While such assays may detect the full length biomarker and the assay result be expressed as a concentration of a biomarker of interest, the signal from the assay is actually a result of all such “immunoreactive” polypeptides present in the sample. Such binding assays may also detect immunoreactive polypeptides present in a biological sample that are complexed to additional species, such as binding proteins, receptors, heparin, lipids, sugars, etc., provided that those additional species do not interfere in binding between the binding species and the target biomolecule. Typically, however, specific binding assays are formulated using purified analyte, and complex formation and fragmentation patterns are not considered. This is particularly true where the identity of such additional binding species are unknown.